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From: ned@pebbles.cad.mcc.com (Ned Nowotny)
Newsgroups: comp.lang.c++
Subject: Re: Sun C++ 2.0 - Default Argument Question
Message-ID: <17237@cadillac.CAD.MCC.COM>
Date: 9 Mar 91 18:33:13 GMT
References: <leo.667062578@galaxy> <DSOUZA.91Feb25171047@optima.cad.mcc.com>
Sender: news@cadillac.CAD.MCC.COM
Reply-To: ned%cad@MCC.COM (Ned Nowotny)
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Organization: MCC CAD Program, Austin, TX
Lines: 89

In article <DSOUZA.91Feb25171047@optima.cad.mcc.com> dsouza@optima.cad.mcc.com (Desmond Dsouza) writes:
=>
=>In article <leo.667062578@galaxy> leo@duttnph.tudelft.nl (Leo Breebaart) writes:
=>
=>	>   The thing is: we are trying to port a project from GNU g++ to Sun C++
=>	>   v. 2.0, and the following type of constructor 
=>	>
=>	>	   SomeClass(String = "woppa");
=>	>
=>	>   generates a "sorry, not implemented: constructor needed for argument 
=>	>   initializer" error. (String is my own implementation of a String class.)
=>	>
=>	>   My main problem is that for the life of me I cannot see a possible 
=>	>   workaround, and of course our code uses dozens of these constructors
=>	>   (which GNU never had any trouble with).
=>	>
=>	>   So:
=>	>
=>	>   1) Is using such a default argument a form of bad programming, and if so,
=>	>      why?
=>	>
=>	>   2) If not, what can I possibly do to get my code running under Sun C++?
=>
=>Make String ("woppa") a static, private member inside SomeClass, and
=>use that as a default in the constructor.
=>
=>	>   Leo Breebaart  (leo @ duttnph.tudelft.nl)
=>
=>Desmond.

Actually, it is easer to just provide a second constructor:

class SomeClass
{
.
.
.
    SomeClass(String);
    SomeClass();
.
.
.
};
.
.
.
SomeClass( String string )
{
.
.
.
}

SomeClass()
{
    String string( "woppa" );
.
.
.
}

In fact, if the argument is just used to initialize a member variable,
the definitions become:

SomeClass( String string ) :
    MemberString( string )
{
.
.
.
}

SomeClass() :
    MemberString( "woppa" )
{
.
.
.
}

In general, overloaded functions are more flexible than default arguments
and, with judicious use of inline'ing, no less efficient.  Except for their
extensive use in existing practice, I would argue for the abolition of default
arguments altogether.

Ned Nowotny, MCC CAD Program, Box 200195, Austin, TX  78720  Ph: (512) 338-3715
ARPA: ned@mcc.com                   UUCP: ...!cs.utexas.edu!milano!cadillac!ned
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